the chase ended when authorities shot and killed 26-year-old tamerlan tsarnaev. nbc's pete williams reports he was run over by the car driven by his brother. and when police approached his body, they discovered an ied strapped to his chest. he was transported to the hospital where he was pronounced dead. let's bring in nbc national investigative correspondent, michael isikoff. let's talk about what we foe in the scene right now. the police have said they have new leads within the last few minutes that they are exploring and that they want everyone to stay inside. >> exactly. a pretty good sign that this situation is still very fluid, still very tense. and we don't know where it's going or how long the manhunt is going to be taking place. i should point out, andrea, that i am right behind what is the principal staging area for the police and the military here. all morning long we had convoys of military humvees coming in, buses of police, motorcycles, of state police, blackhawk helicopters have been flying in and over this area. landing just behind me on the other